Section Archive
Sections below this point are old and are kept for reference.
Resource: Land of Lisp
Lisp has been hailed as the world's most powerful programming language, but its cryptic syntax and academic reputation can be enough to scare off even experienced programmers. Those dark days are finally over — Land of Lisp brings the power of functional programming to the people!
Resource: SICP
MIT's Structure and Interpretation of Computer Programs is a classic in the truest sense; the material in the tome has been used in MIT's programs since 1980, and many of the core concepts have diffused out into reality, becoming the core of our global infrastructure. The book is available for free online in many forms.
Resource: HTDP
How to Design Programs is another MIT classic, with a focus on the program design process over teaching a language.
Other Resources
Common LISP Basics
- Define a global variable with defparameter:
(defparameter *xyz* 18)
- AKA top-level definition, dynamic variable, special variable.
- Don't forget the earmuffs!
(defvar *xyz* 18)will set but not overwrite.
- Define a global function with defun:
(defun func_name (args))
- Functions appear after
(args): (defun example_function () (commands))
- Define and use local varibles with let.
(let ((x 1)(y 2)) (commands))- These variables are only active in the function body.
- Define and use local functions with flet.
(flet ((func_name (args) (commands))) (commands with function))- Again, the function only works in the flet list.
- Multple functions can be defined in the () after flet.
- Like flet, labels defines local functions, but also allows recursive calls.
A simple number-guessing game, using arithmetic shifts (binary search,) can be written like so with a few global functions:
(defparameter *big* 100)
(defparameter *small* 1)
(defun guess-my-number ()
(ash (+ *small* *big*) -1)
)
(defun smaller ()
(setf *big* (1- (guess-my-number)))
(guess-my-number)
)
(defun bigger ()
(setf *small* (1+ (guess-my-number)))
(guess-my-number)
)
(defun start-over ()
(defparameter *small* 1)
(defparameter *big* 100)
(guess-my-number)
)
(start-over)50
In higher-order functions, #'x stands in for (function x).
Here is another example program showing parameters being defined, functions being defined, string insertions, comments, and more:
;;;; Prog5: "Wizard Adventure Game" RCF 2018 - Land of Lisp p.70
(defparameter *nodes*
'(
(living-room
(you are in the living-room. a wizard is snoring loudly on the couch.))
(garden
(you are in a beautiful garden. a well is in front of you.))
(attic
(you are in the attic. there is a giant welding torch in the corner.))))
(defparameter *edges*
'(
(living-room (garden west door) (attic upstairs ladder))
(garden (living-room east door))
(attic (lving-room downstairs ladder))))
(defparameter *objects*'(whiskey bucket frog chain))
(defparameter *object-locations*
'(
(whiskey living-room)
(bucket living-room)
(chain garden)
(frog garden)))
(defun describe-location (location nodes)
(cadr (assoc location nodes)))
(defun describe-path (edge)
`(there is a ,(caddr edge) going ,(cadr edge) from here.))
(defun describe-paths (location edges)
(apply #'append
(mapcar #'describe-path
(cdr (assoc location edges)))))
(defun objects-at (loc objs obj-locs)
(labels
((at-loc-p (obj)
(eq (cadr (assoc obj obj-locs)) loc)))
(remove-if-not #'at-loc-p objs)))
;; Let's run and see:
(describe-paths 'garden *edges*)| THERE | IS | A | DOOR | GOING | EAST | FROM | HERE. |
Catalogue of LISPs
MIT Scheme
The first time you install mit-scheme and run the REPL with scheme,
you'll be greeted with all sorts of hackerisms:
MIT/GNU Scheme running under GNU/Linux Type `^C' (control-C) followed by `H' to obtain information about interrupts. Copyright (C) 2011 Massachusetts Institute of Technology This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Image saved on Saturday December 3, 2016 at 9:44:07 AM Release 9.1.1 || Microcode 15.3 || Runtime 15.7 || LIAR/x86-64 4.118 Edwin 3.116 1 ]=> (exit) Kill Scheme (y or n)? Yes Moriturus te saluto.
MIT Scheme is recommended for learning and applying the contents of SICP.
; To run, execute: scheme < prog6.scm
; SICP Newton's Method for calculating square roots
(define (square x) (* x x))
(define (sqrt x)
(define (good-enough? guess)
(< (abs (- (square guess) x)) 0.001))
(define (improve guess)
(/ (+ (/ x guess) guess) 2))
(define (iterate guess)
(if (good-enough? guess)
guess
(iterate (improve guess))))
(iterate 1.0))
(sqrt 104)
;Value: 10.198039027421274
(square (sqrt 104))
;Value: 104.00000000480743
; Note that all definitions required to run sqrt are included inside the
; definition, meaning they are block scoped and can access lexically scoped
; variable x.GUILE
GNU Guile 2.0.13 Copyright (C) 1995-2016 Free Software Foundation, Inc. Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'. This program is free software, and you are welcome to redistribute it under certain conditions; type `,show c' for details. Enter `,help' for help. scheme@(guile-user)> (exit)
Racket
Welcome to Racket v6.7. > (exit)
Why use Functional Languages?
To expand my programming horizons, I chose to read a book on CLisp, which was fantastic. After this I began applying functional techniques everywhere else; these languages change the way you approach problems. I'm now reading through SICP and Land of Lisp, and enjoying both immensely.
Whichever LISP you use, I recommend using the rlwrap program to
enhance your working experience. Running, for instance, rlwrap guile
adds history, readline and bracket matching to the REPL, which can be a
huge quality-of-life improvement.